Patent GB-630018-A (GB)
Abstract: 630,018. Electric igniters. K.L.G. SPARKING PLUGS, Ltd., CARINGTON, C. M., SHOOBERT, G. W., and BLIGHT, D. J. Nov. 18, 1946, Nos. 34170/46, 25315/47 and 30573/47. [Class 75(iii)] In an electrical ignition device for igniting a fuel jet controlled by a magnetically operated valve in series with a delay-actionswitch, a high voltage is supplied to an igniter filament during the operating time of the delay-action-switch and a lower voltage is supplied to the igniter filament when the delay-action-switch operates to open the fuel valve. As shown in Fig. 2 when the master switch 31 is closed relays 37, 39 are energised to connect a filament 34 which ignites the jet from a fuel nozzle 35a and a heater 33 heating a bi-metallic two position switch 32 to high voltage tappings on a battery 30. When the igniter filament 34 attains its operating temperature the switch 32 changes to its other position thereby connecting the heater 33 and the igniter filament to lower battery voltages through relays 36, 38 and energising a solenoid operated fuel valve 35 to supply fuel to the nozzle. In a modified circuit (Fig. 1 not shown) the relays 36 ... 39 are omitted and two tappings on the battery are connected to a thermally operated two position switch which, at starting, connects the higher voltage to both the igniter filament and a heater for the thermal switch and later connects the lower voltage to these elements and simultaneously energises the solenoid of the fuel valve. Fig. 3 shows a circuit comprising an igniter filament 44 and a coil 48, a resistance 43 of constantan wire and a coil 47 arranged to form a parallel circuit which is connected to a battery through a three pole two position switch 42 operated by a relay 46. At starting the switch 42 is in the position shown and connects the parallel circuit to a high voltage tapping on the battery. Whilst the igniter filament 44 is heating the resistance of the filament branch of the parallel circuit is less than that of the resistance branch so that a differential relay 51 comprising the two coils 47, 48 and an armature 49 breaks the circuit of the relay 46; the relay 46 is slugged so that it does not operate the switch 42 before the armature 49 moves. When the filament 44 attains its working temperature the currents in the two coils 47, 48 are equal and the armature 49 is returned by a spring 50 to close the circuit of the relay 46. The relay then operates the switch 42 whereby a lower voltage is applied to the parallel circuit and the solenoid 45 of the fuel valve is connected to the battery. The first Provisional Specification describes a circuit in which the operating voltage of the igniter filament is the same as its starting voltage, the circuit including a single pole make and break type of bi-metallic switch which when heated by an electrical heater connects the solenoid of the fuel valve to the battery. The first Provisional Specification also states that the heater for the switch and the igniter filament may be connected in series, that the jet when ignited may be used as a torch for igniting a main fuel supply and that the bi-metallic switch may be replaced by a solenoid operated switch with a dash pot or by a spring-operated switch with a dash pot mechanically connected to the master switch. In the second Provisional Specification a circuit similar to Fig. 2 is described. a relay being included to operate the solenoid of the fuel valve and it is stated that the heater resistance may operate by expansion the switch which changes the supplies from the higher to the lower voltages. The third Provisional Specification states that the means for switching the igniter filament supply from the high to the low voltage may include a temperature responsive element whose coefficient of resistance may be either positive or negative.